Work has been directed toward fulfilling the original overall objective to obtain information to provide a better understanding of the inter-relationship between a primary tumor and the tumor specific immune response of a host. One aim is to determine the effect of C. parvum (CP) on in-vitro cytotoxicity of regional (RLN) and non-regional lymph node (NRLN) cells from animals having a tumor present or from which a tumor had been removed. Evidence was obtained to indicate that CP augments in-vitro cytotoxicity of RLNCs and NRLNCs. Following primary tumor removal, RLNs and NRLNs become progressively less responsive to a second exposure of tumor. Administration of CP together with a second tumor can fully restore lymph node cytotoxicity even when almost complete loss of that response to tumor alone exists. In animals whose LNCs are still capable of responding to a second tumor challenge the administration of CP and tumor produces a synergistic augmentation cytotoxicity. Inoculation of 2 doses of CP without tumor antigen restores cytotoxicity to levels achieved by a second tumor exposure. One or two doses of CP to normal animals having been exposed to tumor failed to result in cytotoxicity by LNs from such animals, indicating the specificity of the immune response. We evaluated the effect of BCG on macrophage colony production in tumor bearing animals to determine whether its action might be related to increased generation of macrophages. Macrophage production by bone marrow cells was transiently enhanced by BCG or by a growing tumor. When the effect of either has disappeared, the combination of the Z results in those cells continuing to produce a significantly greater number of macrophages. Experiments were directed toward evaluating the effects of the prolonged administration of CP alone and in combination with CY for treatment of established measurable C3H tumors. Investigations will be continued to (a) evaluate the effect of a growing tumor and its removal on cultured macrophage cytotoxicity, (b) evaluate the effect of tumor removal and the effect of a second tumor on persistence of blocking factor, (c) determine effect of presence or absence of a primary tumor in the effectiveness of chemo-immunotherapy of metastases and (d) determine whether findings in c. (above) can be related to a. and b. (above).